您好，如果您拿了对方东西，而且对方没有赠与的情况下，有义务归还，otherwise you may have committed an offence for conversion.
关于是否有权利搜查您的车，下面的章节可能对您有一些帮助：
When can the Police stop and search me?
The Police have a broad range of powers to search and seize property, depending
on a range of different factors.
If the Police stop you on the street, you should give them your correct name and address if they ask, but you are not generally bound to answer their questions. They can't search you unless:
•
you let them, or
• you are arrested, or
• they have a search warrant, or
• there are reasonable grounds to suspect you have drugs or an offensive weapon on you, or
• you are in a public place where there is a liquor ban and they are searching for alcohol, or
• you are in transit (i.e. in an airport, railway station or other such place) and they have reasonable grounds to believe that you have property that has been stolen or unlawfully obtained.
The Police have special powers to search under the Misuse of Drugs Act and the Arms Act - but they must tell you that they are using those powers when they search you if they don't have a search warrant.
They do not need a search warrant to search a vehicle if they believe any property that is stolen or obtained by a crime involving dishonesty is in the vehicle.